This study will attempt to further define the primary factors involved in sodium balance in normal and edematous states. A substantial body of evidence has accumulated which suggests that the collecting duct is of major importance in this complex regulatory mechanism. Therefore, experiments will be designed to evaluate collecting duct sodium transport in a variety of experimental circumstances. Free flow micropuncture, direct papillary punctures, and microinjection techniques will be utilized to determine the effect of vascular and/or interstitial volume expansion, renal vasodilatation, aldosterone and prostaglandin release on collecting duct sodium transport in normal rats and rats with either thoracic vena caval obstruction or chronic arterio-venous fistula. Special emphasis will be placed on evaluating one possible determinant of collecting duct sodium transport, alterations in prostaglandin release. In addition to the studies listed above, the isolated tubular perfusion technique will be used to determine the effect of varying serosal concentrations of Prostaglandin E. on cortical collecting tubule sodium transport. The factors involved in the release and synthesis of PGE will be determined in the kidney of the rabbit utilizing radioimmunoassay techniques. Also balance techniques will be performed in normal and edematous rats to determine the effect of prostaglandin release on sodium balance. The role of the collecting duct in the regulation of potassium transport is still not clear. Similar direct papillary punctures and microinjection techniques will be utilized to determine the effect of tubular flow rate and other parameters on collecting duct potassium transport.